1. Field of the Invention
The present invention relates to a digital information signal reproducing apparatus applicable to audio signal processing in a digital VTR which records/reproduces digital video signals and digital audio signals.
2. Description of the Prior Art
For a digital video tape recorder VTR which records/reproduces a composite digital color video signal and a digital audio signal, there is a digital VTR standard based on D-2 format authorized by the SMPTE (Society of Motion Picture and Television Engineers). According to this standard, first and second identical copies of an input digital audio signal are recorded at head-leaving end portions of a first track or tracks and at head-entering end portions of a second track or tracks adjacent the first track or tracks. The two digital audio copies are separately decoded and output, and the decoding scheme utilizes both the first copy and the second copy. Specifically, since two copies of identical data are recorded as a first copy and a second copy, data having no errors are selected from the first copy and the second copy to construct a code block of outer codes by referring to an error flag provided by inner code decoding. With respect to this outer code block, the correction of the outer codes results in the improvement of error correction processing.
Using this digital VTR standard, variable speed reproduction in which the tape speed is different from that at the time of normal mode is possible. At the time of variable speed reproduction, a scanning trace of a rotary head does not coincide with an inclined recording track. However, in the above case where the tape speed is several times for the normal reproducing mode, the rotary head is displaced transversely relative to the recording track by piezoelectric elements so that the scanning trace of the rotary head coincides with the track. Such a tracking technique is called "dynamic tracking".
At the time of variable speed reproduction, for example, at the time of double speed reproduction, such dynamic tracking is used so that the rotary head scans a group of tracks on which one field signal is recorded. Then, the head jumps over tracks on which the next field signal is recorded and scans the tracks on which a following field signal is recorded. As a result of this track jump, the contents of the audio data of the first copy reproduced just prior to the track jump do not coincide with the contents of the audio data of the second copy reproduced immediately after the jump. Consequently, erroneous error correction processing results if the decoding using the first copy and the second copy is based on an error state similar to the one in normal reproduction.
To avoid the erroneous correction processing, only the audio data of either the first copy or the second copy are used as a reproduced output at the time of variable speed reproduction. As a result, a problem exists in that error correction capability is lowered as compared with that in normal reproduction.